I have a 2004 Electric Glide Classic. It has a screaming eagle kit installed ( Not sure what that does as of yet ) I'm a newbie... Anyway there is a Vacuum Connection on the side probably a 3/8 fitting maybe a little smaller. there is no hose connected to it. The bike appears to run fine. Does anyone have the Diagram for Vacuum connections or should I just plug it so there is not dust or water sucked in ?

 

How about a picture?? Screaming eagle kit is a little vague as the are a number of different screaming eagle kits.

 

I will take pic tomorrow and post it.

 

Is the port on the throttle body? Yes, cap it.

 

Not sure if attachment is attached.

 

If it's the one with the cap on it in the pic then yes cap it..

 

I am guessing since you say SE but on most regular bodies, this is the purge line fitting for the carbon canister on CA bikes. Yes, plug, any open vacuum lines. Surprised an SE is legal in CA and would have that.
And don't plug it with the light duty cap you get at Auto Zone. Heat will soon harden it and it will fall off. Probably what happened to yours. Get the real cap at Harley.